Modifying (amplifying or attenuating) electromagnetic signals is, generally speaking, a function of an electrical component or system. Modification may be useful in any number of systems, and is generally done by linear or non-linear techniques. Linear techniques generally provide an output signal with a relatively close resemblance, except for scale, to an input signal. Non-linear techniques generally provide an output signal, which does not have a relatively close resemblance to an input signal.
Either non-linear or linear amplifiers may be useful. Non-linear amplifiers may be useful for on/off amplification—that is, where there is no need to produce an accurate amplification of an input signal, but merely amplify a signal. Linear amplifiers may be useful where an accurate, amplified reproduction is desirable.
When accurate reproduction is desired, therefore, a linear amplifier has been desirable. However, the poor efficiency of a linear amplifier may make its use undesirable in some situations. Efficiency refers to the ability of the amplifier to translate DC power input into power output. A linear amplifier is less efficient than a non-linear amplifier because it draws more power than a non-linear amplifier to output a signal with the same strength. Moreover, a linear amplifier requires quiescent current, or current from a power source even when not amplifying. In applications with a limited power source, such as battery power, a non-linear amplifier may be desirable, as a non-linear amplifier typically requires very little or no quiescent current.
In some areas of signal processing, however, such as radio frequency (RF), non-linear techniques lead to less than desirable results. For example, although linear amplifiers are desirable in RF receivers because of their signal reproduction accuracy, the power draw required by linear amplifiers limits their usefulness, especially in portable, battery driven devices.
Attempts have been made in the art to overcome these difficulties. For example, amplifier combining—using multiple amplifiers to amplify the same signal—is one method that attempts to leverage linear and non-linear benefits. However such attempts to date have been constrained by various difficulties. For example, amplifier combining methods use components, such as transformers or quarter wave lines, to sum the output of the amplifiers in order to drive the load. These components add to the cost and size of the amplifier array.
Accordingly, it would be helpful to the art of signal modification if linear amplifier techniques could be used in combination with non-linear techniques in order to provide effective amplification techniques.